The reaction of carboxylic acids with vinyl acetate monomer (VAM or VA) to make vinyl esters is well known in the literature. The earliest art teaches transvinylation using a mercury catalyst. See U.S. Pat. No. 2,997,494 to Brown, U.S. Pat. No. 3,000,918 to Wilip, et al., and U.S. Pat. No. 3,337,611 to Bearden, Jr., as well as Slinckx et al., Tetrahedron, Volume 22, Issue 9 (1966) Pages 3163-3171 and Slinckx et al., Tetrahedron, 23 (1967) 1395-1403. U.S. Pat. No. 2,245,131 to Herrmann et al. teaches vinyl acetate and benzoic acid transvinylated using a mercury/sulfuric acid catalyst under reflux, and then the volatiles were removed by distillation prior to distillation to recover vinyl benzoate. British Patent No. GB 1486443 to Imperial Chemical describes a transvinylation reaction for the production of a vinyl ester of an organic carboxylic acid by transvinylating a vinyl ester of an organic carboxylic acid with an organic carboxylic acid whose vinyl ester has a lower boiling point than the vinyl ester reactant. Mercury salts are no longer in use due to the toxic nature of mercury-based compounds.
The literature suggests that the preferred catalysts for transvinylation reactions have been mercury- and palladium-based compounds. Transesterification is disclosed by McKeon, et al., Tetrahedron, Vol. 28, p. 227, 1972, Part I. McKeon, et al. show the vinyl interchange reaction between a vinyl ether and an alcohol using a palladium catalyst in a liquid phase batch process. Nitrogen ligands are used to stabilize the catalyst (pyridine). See also McKeon, et al., Tetrahedron, Vol. 28, p. 233, 1972, Part II in which a catalyst precursor is disclosed of either palladium acetate phenyl or palladium acetate biphenyl complexed with monodentate ligands for stability. However, the resulting catalyst was ineffective. Two catalysts prepared were diacetato (2,2′-bipyridyl)palladium(II) and diacetato (1,10-phenanthroline)palladium(II). Vinyl laurate was prepared from lauric acid and vinyl acetate using the palladium acetate complex with 2,2′-bipyridyl. Schultz et al., Journal of Catalysis, 16 (1970) 133-147, discuss the catalyzed decomposition of vinyl acetate into acetic acid and acetaldehyde using a palladium(II)-chloride catalyst. Palladium catalysts are more specifically applied to transvinylation as described in U.S. Pat. No. 3,188,319 to Smidt et al., U.S. Pat. No. 3,755,387 to Young, and U.S. Pat. No. 4,425,277 to Kawamoto et al., as well as Ketterling et al., Applied Catalysis, 66 (1990) 123-132, Waller, Chemical Industries (Dekker) 1994, 53 (Catalysis of Organic Reactions), p 397, Molecules, May 1, 1999 (Iranian Paper), European Patent No. EP376075, and Japanese Patent Nos. JP1994-9492A to Mitsubishi Rayon Co. Ltd., JP1995-138203 to Fuso Chemical Co. Ltd., and JP1999-171837 to Nippon Steel Chemical Co., Ltd. U.S. Pat. No. 3,188,319 to Smidt et al. further discloses use of platinum and rhodium catalysts for less effective transvinylation of various carboxylic acids in a liquid phase with no solvent after forming from a metal chloride or acetate precursor. Ketterling et al. disclose palladium acetate diimine complexes, such as palladium acetate complexes with 2,2′-bipyridine, as catalysts for transvinylation of unsaturated and saturated carboxylic acids. Sabel et al., Chem. Ber. 102, 2939-2950, 1969, describe Pt(II) and Rh(III) used to catalyze a transvinylation reaction. U.S. Pat. No. 4,425,277 to Kawamoto et al. discusses a method for the preparation of alkenyl esters of carboxylic acids, such as benzoic acid, using the combination of a catalyst, such as palladium acetate, and a redox agent. Transvinylation to produce a carboxylic vinyl ester is also taught in Japanese Patent Nos. JP2002-322125 and JP2002-322126 to Japan Vam & Poval Co., Ltd., which describe combining the reactants, palladium acetate catalyst and lithium acetate co-catalyst together and reacting the mixture at 65° C.
Use of ruthenium catalysts in transvinylation is also known in the art. See U.S. Pat. No. 5,155,253 to Murray, as well as Murray & Lincoln, Catalysis Today, 13 (1992) 93-102, which provides a summary of previous patents and Chem Systems Vinyl Neodecanoate (90S8), February 1992, which provides a review of ruthenium transvinylation as well as addressing palladium catalyzed transvinylation. U.S. Pat. No. 4,981,973 to Murray discloses that ruthenium compositions are useful transvinylation catalysts for numerous Bronsted acids and derivatives of Bronsted acids. However, the Murray processes require a carbon monoxide atmosphere, which requires careful handling.
Iridium catalysis, with a NaOAc additive, of liquid phase batch transvinylation of benzoic and other acids with a substituted alkyne is described by Nakagawa, et al. in Tetrahedron Letters 44 (2003) 103-106. The iridium catalyst is formed from a [Ir(cod)Cl]2 precursor.
U.S. Pat. No. 5,210,207 to Mokhtarzadeh, et al. teaches continuous transvinylation by reactive distillation. Mokhtarzadeh, et al. discloses a process for the preparation of numerous vinyl derivatives of Bronsted acids formed by the transvinylation reaction of a vinyl derivative of a first Bronsted acid and a second Bronsted acid wherein the vinyl product ester is less volatile than the vinyl reactant ester. In particular, Mokhtarzadeh, et al. teaches reacting vinyl acetate and benzoic acid to produce vinyl benzoate or reacting vinyl acetate with 2-ethylhexanoic acid to produce vinyl 2-ethylhexanoate. See, particularly, Examples 4 and 8. Mokhtarzadeh, et al. further provides for removal of the reaction product from the column to avoid reflux and thus aid the reactive distillation process; reactants are recycled to the reactor. Ruthenium catalyst concentrations of from about 30,000 ppm to about 0.01 ppm based on the weight of the liquid phase reaction medium and reaction temperatures of from about 20° C. to about 300° C. are disclosed, with a ruthenium concentration of 50-75 ppm and a temperature of 125-135° C. disclosed in Examples 4 and 8, and a temperature of 140-145° C. disclosed in Example 3. However, the Mokhtarzadeh process achieves poor yields.
U.S. Pat. No. 6,891,052 to Tanner et al. teaches formation of a vinyl ester using a zinc carboxylate catalyst and acetylene gas. Tanner et al. teaches batch operation at a temperature of about 205° C. See Examples 1 and 2, which exemplify synthesis of vinyl neodecanoate.
European Patent No. 0648734 A1 to Packett discloses synthesis of higher vinyl esters directly from ethylene in the presence of palladium cupric salt catalysts, but achieves very low yield. See Examples 2-11, 22, 26-27, 29-32, 36-39 and 41-43, wherein vinyl 2-ethylhexanoate is prepared at yields of up to 69%; Example 12 which discloses production of vinyl butyrate; Examples 18, 25 and 34, wherein synthesis of vinyl neodecanoate is disclosed in yields up to 37%; Examples 19 and 35, wherein synthesis of vinyl benzoate in yields of 21% is disclosed; Examples 20-21, in which synthesis of a mixture of vinyl adipate compounds having a combined yield of up to 46% is disclosed.
U.S. Pat. No. 5,223,621 and EP 0 494 016 B1 to Vallejos et al. teach transvinylation of carboxylic acids, including benzoic acid, with VAM in the presence of a catalyst and ligand in a system that incorporates reflux. Vallejos et al. disclose a palladium acetate (II)—2,2′-bipyridyl complex catalyst formed in situ in a mole ratio of 2,2′-bipyridyl to palladium (II) acetate of about 3:1. See particularly Examples 6 and 8. In example 8, Vallejos et al. describes using 8721 ppm of palladium equivalent per kg of benzoic acid and a VAM to acid ratio of 5:1. After a reaction time of 6 hours, the process according to Vallejos et al. achieved a yield of 89%. The transvinylation reaction disclosed by Vallejos et al. provides a TON of 0.12 kg VB/g Pd. However, the combined use of palladium (II) acetate and 2,2′-bipyridyl is only described in Example 6. The catalyst recovery taught by Vallejos et al. involves precipitation and filtration of palladium from the reaction medium, after which the product is removed by distillation. The temperature of the reaction is held at or below 100° C. to maintain catalyst stability.
U.S. Pat. No. 5,214,172 to Waller discloses catalytic transvinylation of a carboxylic acid to form a vinyl ester. Waller further teaches reactants including vinyl acetate and aliphatic and aromatic mono-carboxylic acids reacted in the presence of a palladium catalyst introduced to the reaction mixture as palladium acetate complexed with an aryl N-containing ligand, such as 2,2′dipyridyl or 1,10-phenanthroline. However, Waller only provided working examples for transvinylation of stearic acid and dicarboxylic acids including suberic, adipic, glutaric, and succinic acids, and found the catalyst complexes having 2,2′-dipyridyl or 1,10-phenanthroline ineffective for use with dicarboxylic acids.
U.S. Pat. No. 5,741,925 to Mao et al. teaches transvinylation of naphthenic acids, which are classified as monobasic carboxylic acids of the formula CnH2n-zO2, where n indicates the carbon number and z is zero for saturated acyclic acids and 2 for monocyclic acids, for example, with a vinyl ester, such as vinyl acetate. The process of Mao et al. is directed primarily to C10 to C20 carboxylic acids, as evidenced by claims 2 and 8. Catalysts used in the transvinylation process of Mao et al. include palladium acetate complexed with one or more aryl N-containing ligands, such as 1,10-phenanthroline or 2,2′-dipyridyl. Mao et al. further teaches that the catalysts can be recycled over several uses.
From the foregoing, it is clear that the existing processes utilize toxic catalysts such as mercury catalysts and/or are not appropriate for economically viable industrial scale operations. Furthermore, there is an unmet need for economically viable catalysts that produce vinyl esters with high selectivity, high conversion and in short reaction campaign times from the reaction of VAM and other carboxylic acids in a continuous or semi-continuous operation.